The disclosed invention generally relates to pivot structures, and particularly to a flexural pivot structure which is particularly useful in apparatus for bonding thin wire leads in microelectronic circuits.
2. Background Art
In the manufacture of microelectronic circuit packages, certain electrical connections are made with extremely thin gold or aluminum wires. For example, connections between a semiconductor integrated circuit chip and the package leads are typically made with such thin wires. As another example, active elements in semiconductor hybrid circuits may be interconnected with extremely thin wire.
The attachment of interconnecting thin wires is typically accomplished with wire bonding machines which supply wire and make the connections of the opposite ends of the wire leads. Generally, a wire bonding machine includes a bonding head which can move vertically, horizontally and rotatably about a vertical axis. A transducer (e.g., an ultrasonic transducer) is pivotally mounted to the bonding head so as to pivot about a horizontal axis, preferrably at the center of gravity of the transducer and its mount. The transducer includes an arm portion with a bonding tool at its end. The bonding tool is raised and lowered relative to the work piece by vertical movement of the bonding head. When the bonding tool contacts and withdraws from the work piece, the transducer arm pivots. Ideally, in the vicinity of contact with the work piece, the bonding tool should travel in a straight line perpendicular to the workpiece bonding surface.
In presently known systems, due to clearance requirements, transducer arm pivot structures are mounted to constantly remain above the plane of the work piece. Therefore, the pivot action resulting from lowering and raising the bonding tool will cause undesirable tip skid due to non-perpendicular motion in the vicinity of contact with the workpiece. In some present systems, the effects of tip skid are reduced, but not eliminated, by having long transducer arm portions between the pivot axis of the transducer arm and the bonding tool. However, such long arm portions result in more difficult control of the positioning of the bonding tool. Moreover, if the bonding tool requires specific positions to accomplish wire feed between the first and second bonds, a long transducer arm would possibly make such required positions difficult, if not impossible.